This invention relates to user-assisted identification of object boundaries in a raster image.
A raster image, such as that illustrated in FIG. 1, is defined by rows and columns of pixels. In a raster image such as FIG. 1, an object boundary may be defined by identifying the pixels forming the object boundary. Once identified, the object within the boundary can be extracted and digitally manipulated for various uses in image composition.
Pixels falling on the object boundary are typically identified by a high contrast in pixel values between pixels on the boundary and pixels just outside the boundary. For example, FIG. 1 illustrates a raster image of a ball illuminated by light coming from the top. The pixels forming the boundary segment (identified in FIG. 2 as 110) of the ball (identified in FIG. 2 as 100) facing the light are easily identified because there is a high contrast between their values with the values of pixels forming the background. Pixels forming the boundary segment (identified in FIG. 2 as 120) on the bottom of the ball, however, are less easily identified because the values of pixels defining that boundary segment are similar to the values of pixels forming the surrounding background.
User input can assist in the identification of object boundaries, including boundary segments that are not readily detected.